On-load tap changers make it is possible to change the taps of windings of a step transformer under load without interrupting current flow. Off-load tap changers facilitate the switchover between winding taps of a step transformer when not under load. Movable-core coils allow impedance to be changed or adjusted.
Position-signaling apparatuses functioning as part of the motor drives of on-load tap changers or the like serve to determine the current position of the on-load tap changer or the like and to output this position; this is in turn the starting point for the--normally optical--display of the position and is also usable as an actual value for subsequent control functions.
Known position-signaling apparatuses for on-load tap changers comprise a circular array of signaling contacts each corresponding to a respective position of the on-load tap changer or the like. The signaling contacts are engaged by a centrally rotatable signaling contact lever that is connected with the on-load tap changer or more accurately with the motor drive of the on-load tap changer. In this manner the signaling-contact lever is moved with each change in operational position of the on-load tap changer, that is on switching from one winding tap to another, is only moved through an angle that corresponds to the spacing between two adjacent signaling contacts. As a result of the continuous movement of the signaling contact lever there is a very slow contact separation that depending on the switching operation can take several seconds. Such a position-signaling apparatus is thus not suitable when the signaling contacts are fed with a direct-current circuit or are required to transmit high currents.
German 1,812,609 shows a more developed position-signaling apparatus wherein in order to increase the switching capacity each individual contact has its own snap switch. This solution is however very expensive.
In order to simplify the system of German 2,108,013 a position-signaling apparatus is provided where there is only one such snap switch arranged in the circuit instead of the many snap switch and it is actuated by means of a cam disk that is coupled via a transmission with the signaling contact lever. Even this arrangement is somewhat expensive as two separate rotations must be created: on the one hand for the actual movement of the signaling contact lever from one signaling contact to the next, also with n possible positions through an angle of (360/n).degree.; on the other hand the movement of the cam disk that must for each switching turn through an angle of 360.degree., that is through a complete revolution.
For further simplification it is known from German patent 2,947,343 to mount the one provided snap switches for the position-signaling apparatus on the rotatable signaling contact arm. Actuation of the snap switch is effected by a concentric cam formation that extends in a circle around the signaling contact.
This arrangement has the disadvantage that the movable signaling contact cannot be made as a simple bridge since, as described, it carries the snap switch, and a series connection between the signaling contact, snap switch, and signaling contact to the contact arm is required. In addition the electrical connections to the snap switch complicate this arrangement since the snap switch orbits with the signaling contact lever, is therefore not stationary. In addition this known arrangement cannot be made as a printed circuit.
In general these known position-signaling apparatus are to complicated either in their actual structure on in their manufacture.